Composite diamond grain

Abstract

A composite diamond grain which comprises a heat-resistant grain as a nucleus and discrete diamond crystal particles distributed on the surface of the grain or diamond crystal films formed to cover the entire surface of the grain and a method for producing the composite diamond grain by the vapor-phase process are disclosed. For the filament method which is one form of the vapor-phase method, tantalum is useful as the material for the filament. Since tantalum is susceptible of embrittlement by hydrogen, a treatment to be performed on tantalum for the elimination of this drawback is also disclosed.

We claim: 
     
       1. A composite diamond grain, comprising a heat-resistant grain at least 30 μm in diameter and discrete diamond crystal particles at least 0.1 μm in diameter and deposited and dispersed on the surface of said heat-resistant grain so as to occupy 10 to 90% of the total surface area of said heat-resistant grain. 
     
     
       2. The composite diamond grain according to claim 1, wherein said discrete diamond crystal particles occupy 30 to 80% of the total surface area of said heat-resistant grain.